1. Technical Field
The present invention relates to a run flat tire and a method for producing the same.
2. Related Art
There is a pneumatic tire called a run flat tire that can run in a certain extent of distance even in the state that air pressure in a tire has reduced and reached 0 kPa by tire failure such as puncture. It is known to reinforce a side wall part by providing a side reinforcing rubber part on an inner surface of the side wall part as a technique for enabling run flat running in the state that an inner pressure has reduced as above (for example, see US2006/0219343A1 and JP-A-2008-189911).
In a run flat tire of such a side reinforcing type, high rigidity rubber is used in a side reinforcing rubber part to suppress deformation of a tire during run flat running. However, a temperature of a side reinforcing rubber part is increased during run flat running, and as a result, rigidity of the side reinforcing rubber part is decreased, resulting in decrease of run flat durability. On the other hand, where decrease of rigidity of a side reinforcing rubber part at high temperature is suppressed, stress applied to a bead part is increased during run flat running, and strain in the bead part is increased. For this reason, separation occurs between bead filler and a carcass ply, and run flat durability is sometimes decreased.
JP-A-2004-276699 and WO2010/074286 disclose that to suppress peeling between a side reinforcing rubber part and an inner liner layer during run flat running, covulcanizability is improved by specifying the difference of vulcanization rate between those. Furthermore, US2008/0295941A1 discloses that to suppress peeling between a side reinforcing rubber part and a carcass ply, a rubber sheet having an intermediate vulcanization rate is arranged between those. However, JP-A-2004-276699 and WO2010/074286 focus on vulcanization rate calculated from the difference between 90% vulcanization time and 10% vulcanization time, and do not intend to improve run flat durability by focusing on time until initiation of vulcanization. Furthermore, those three patent documents do not disclose to specify vulcanization time between bead filler and a carcass ply in order to suppress fracture of a bead part during run flat running.